Production of isocyanates from substituted ureas



"PRODUCTION OF IsocYANAT s' FROM SUBSTITUTED UREAS I Robert J. Slocombe, Dayton, Ohio, and James H; Saunders, Anniston, Ala tassignors to Monsanto Chemical Company, St. Louis,aMo.,--a corporation of Delaware No Drawing. Application January 19, 1953,

Serial No. 332,086,

' 13 Claims. (Cl. 260--453) The present invention is directed to monocarbamyl halides and isocyanic acid esters and to an improved method of producing same.

An object of the invention-is to provide an economical- 1y and commercially feasible method of making monocarbamyl halides and isocyanic acid esters in good yields.

Another object of the invention is to provide a method [of making monocarbamyl halides and isocyanic acid esters from readily available starting materials. t

Another object of the invention is to provide a method of making monocarbamyl halides and isocyanic acid esters without the useof phosgene, thus Overcoming the disadvantagesand difl'iculties which accompany the use of this toxic gas.

A further object of 'the invention is to provide a continuous method, of producing monocarbamyl halides and isocyanicacid esters from NeiIlOIlOSllbStltUlCdOl N,N'- hisnbstituted ureas and hydrogen halides;

Other objects and advantages will be a'pparentito those skilled: in the art asl'thewdscription of :theinven'tion proceeds Q s 1 I 1 ,:In accordance with the instant invention, the above objectszire' accomplished by reacting,.in the vaporphase, :N-monosubstitutedbi N,N='-'d isubstituted ureas with hydrogen halides in accordance with the tollow'ing equa- Rasmussen's wherein: R and are the same or different organic rad- I ica ls and X is a halogen atom, preferably chlorine and bromine. I v p In-the above reactions, the product recovered maybe the monocarbarnyl halide; or the corresponding-isocyanic acid ester, depending'upon the-hydrogen halidei'urea motheone; hand,'rf"t:h'e molar ratio of hydrogen halide to urea is greater than 1:1 or is at least 2 1j, condensation 'ofi'the" gaseous or vaporous' product causes the is'ocyanic acid es'terand excess hydrogen halid'eto combine 'to form mixtures of the above estera'nd the clor'responding monocarb amyl halide or" a product consisting essentially of th carba myt hafide. Moreover, if the hydrogen halide in excess of that requiredto form ammonium halide or airline hydrohali'de is separated from the gaseous or vapqrou's product at a temperature or under conditions L v 2,773,086 Patented Dec. 4, 1956 avoiding substantial combination 'of the ester withf tlie hydrogen halide, then the *isocyanic acide'st er ares-av; ered. Theseparation of th isocyanic acidesters' from the unreac'ted hydrogen halide is accomplished'byph ical and/or chemical means, but the most .pract l method to be used varies with 'the"isocyanic ester "pr duced. V Thus, if the isocyanic acid ester boils abov' e' the decomposition temperature of the correspohdrn ca baniyl halide, the separation may be advantageously efiected by chemical or physical means "such as by condeiisi'h tir scrubbing the ester from the-reaction products a 'te perature above that at which the carbarnyl h'l dis ates to hydrogen halide and isocyanate' However, if the ester boils in the range of 'or belowfthe' carbam'ylj halide decomposition temperaturejthen chemical.,methods' The apparatus empldyedinthis embodiment-of me -in vention included a tubular. reactor, a receiver partially filled with toluene, a packed tower mounted on the receiver and communicating therewith and a recycle line including a centrifugalpump for withdrawing toluene from the receiver, and pumpin itinto at the packedtbwer so that the above solventcotild scrrib me gaseous for vaporo'us "reaction product. The "scrubbing solvent thus enriched "was then returned to. the receiver to be. continuously recycled" to' the scrubbingtower, and

the uncondensed gasesryvere discharged from the sys;

tem by an exhaust gas line" which was attached to the top of the above tower. p a

The tubular reactor consisted of an electrically heated Pyrex glass tube which Was-l inch in diameter and 18 inches in length. About two inches fromthe feed end of the reactor, there was provided an inlet tube for, in troducing nitrogen and "finely divided N,N"-diphenylfirea, and about 5 inches frorrithe Same end, h 'reactoriwas equipped with an inlet tube forintroducihg hydrogen chloride so that it-could reactwith the'vaporized MN- diphenyliirea. More r, th .e reactor waserevidetrgtvnh a thermometer which extended from the, feed end. of the reactor to a point just ,beyondJthehyd'rogen chloride inlet tube; so tha't themeaction, temperature could be measured bln addition, in'theljreactor and beyondl the end of the thermometer, Be'rl saddles were introduced so as to facilitate intimate mixing of thereacta-nts. Final- 1y, the ex'i'fIe nd of the reactor was directlyconuected to thetOIuene-comaining receiver in -such a. manner that the gaseous or vaporous product was passedover the surface of the toluene and then was conducted into the packed tower where it was treated: with a countereurrent stream of the recycled toluene.

.Nitrdgen under slight pressure was intrpduced r g with the symmetrical disubstituted urea so as to; li tate the mmn'gerxthe aaer with. the hydrogen chloride andalsov to prevent the .hydrg n chloride from flowing in the direction of the ,disubstit uted, urea, inlet tube which was 'found to cause side reactions a substantial -ree i he yield f he d re Produ t:

Description of method N,N'-diphenylurea (49.5 grams), nitrogen and an excess of hydrogen chloride were introduced into the above reactor over a period of hours, during which time the reaction temperature was maintained within the range or about 350 C. to about 360 C. The effluent gases and solids from the reactor were passed'into the scrubbing tower where the phenylcarbamyl chloride, aniline hydrochloride and unreacted N,N'-diphenylurea were recovered by scrubbing with toluene. The gaseous residue including nitrogen and hydrogen chloride was discharged from the system.

' The toluene slurry thus produced was filtered to remove its solids content, namely, the aniline hydrochloride and unreacted N,N-diphenylurea.

The resulting filtrate containing phenylcarbamyl chloride was then treated w th aniline to convert the latter to N,N'-diphenylurea.

23.6 grams of N,N'-diphenylurea wasv obtained, thus showing that the yield of phenylcarbamyl chloride corresponded to 57.6% of theory, basis N,N-diphenylurea.

EXAMPLE II Phenylcarbamyl chloride The procedure described in Example I was repeated, using a reaction temperature of about 350 C. to about 370 C., 48.4 grams of N-phenylurea, and an excess of hydrogen chloride gas.

The toluene slurry thus obtained was filtered to remove its solids content which included unreacted N- phenylurea and ammonium chloride. The resulting filtrate was then treated with aniline and carbanilide was obtained in good yield, thus showing that N-phenylurea had been converted into the corresponding carbamyl chloride, i. e., phenylcarbamyl chloride.

EXAMPLE HI Ethylcarbamyl chloride "The procedure employed in Example I was repeated,

'using 81.5 grams of symmetrical diethylurea, an excess The procedure described in Example I was followed, employing 58.7 grams of symmetrical dicyclohexylurea, an excess of hydrogen chloride gas, a reaction temperature of about 350 C. to about 360 C., and a reaction time of 5 hours.

The toluene solution was filtered, yielding a precipitate of cyclohexylamine hydrochloride and a filtrate containing cyclohexyl carbamyl chloride. This filtrate was distilled under reduced pressure and 23.4 grams of cyclohexyl isocyanate was recovered which amounted to. a yield of 71.5% of theory, basis symmetrical 'dicycloh'exylurea. I 7

Inthe production of monocarbamyl halides and the corresponding isocyanic acid esters in accordance'with the present invention, the hydrogen halideand the N- 'monosubstituted or N,N-disubstituted urea are reacted together in the vapor phase and in a hydrogen halide/ urea molar ratio which may vary from about 1.1 to about 8.0. Larger or smaller ratios are also within the scope of the invention, but when smaller ratios are used, the theoretical requirements for combination with the byproduct ammonia or amine should at least be met.

The above reaction is carried out at a temperature within'the range defined by the boiling point of the N- monosubstituted or -N,'N-disubstituted urea and that temperature which avoids substantial decomposition of the icocyanic acid ester produced. More particularly, the reaction is carried out at a temperature within the range of about 300 C. to about 500 C. and within these limits a temperature of about 350 C. to about 400 C. is preferred.

The product of the reaction between the hydrogen halide and the N-monosubstituted or N,N'-disubstituted urea is --a gaseous or vaporous mixture containing the corresponding isocyanic acid ester. If the hydrogen halide is used in an amount exceeding that required to react with'the by-product ammonia or amine, the isocyanic acid ester and the excess hydrogen halidereact at temperatures below about 60 C. to about C. to produce the corresponding monocarbamyl halide. Therefore, if the isocyanate is desired, it is essential that the excess hydrogen halide be separated from the isocyanate at a temperature at which substantial combination is avoided. Stated in other words, this separation should be effected at a temperature above 90 C. but below the boiling point of the isocyanic acid ester or, preferably, at a temperature above 90 C. but not above about C. However, if the hydrogen halide is employed only in an amount sufiicient to react with the by-product ammonia or amine, no excess hydrogen halide will be present in the gaseous or vaporous mixture, in which case the isocyanate will be recovered directly. The mixture of ammonium halide or amine hydrohalide and isocyanate thus obtained is desirably separated by one of the following methods.

One method involves passing the gaseous or vaporous reaction product into a solid'entrainment separator, e. g., a cyclone separator operated at a temperature such that the solid ammonium halide or amine hydrohalide is separated and the isocyanate is passed on with the gas stream. This gas stream is further cooled and scrubbed with toluene or another suitable solvent to effect a recovery of the isocyanate. 7

Another method comprises collecting the ammonium halide or amine hydrohalide and isocyanate in toluene, hexane or another suitable selective solvent for the isocyanate, filtering to remove the ammonium halide or amine hydrohalide and then distilling to separate the isocyanate from the solvent.

The isocyanic acid esters containing from 2 to 5 carbon atoms per mol boil in the range of or below the carbamyl halide decomposition temperature and may be separated from hydrogen halide by scrubbing with a tertiary amine or a solution thereof in an inert organic solvent for the ester such as chlorobenzene, xylene, toluene, orthodichlorobenzene, 1,2,4-trichlorobenzene', kerosene, cyclohexane, carbon tetrachloride, hexahydrobenzene, ligroin, petroleum, etc. The'separation of the above esters from the hydrogen halide may also be effected by adsorbing the hydrogen halide in an adsorbent or any of the well-known means for, physically separating the above gas from gaseous products containing'same.

The isocyanic acid esters containing at least 6 carbon atoms per mol boil above the decomposition temperature of the corresponding carbamyl halide and may be readily separated by condensing and/or scrubbing the esters from the reaction product at a temperature above the decomposition temperature of the corresponding carbamyl halide, but other-well known physical methods of separating hydrogen halide from gases containing same are also within the scopeo f the invention.

If desired, the hydrogen halide and the N-monosub- ,stituted or N,N-dis'ubstituted urea may be reacted together in the vaporphase and. in the proportions required to form a vaporous orgaseous mixture of isocyanic acid ester, by-product ammonium halide or. amine hydrohalide and unreactedfhydrogen halide, which product is then permitted to condense so as to recover the corresponding carbamyl halide by chemical'union of the-ester with the unreacted hydrogen halide. The carbamyl halide may then beoonverted into the corresponding isocyanate and the method employed for this purpose is dependent upon h -relationship between the bo in PQint .of the isoyanate and e decomp tion t mpe ature o the ea bamyl halide. If .the rboiling point of the isocyanate. is

\ above the decongposition temperature-of ,the carbamyl halide, then the conversion may be carried outthermally without a dehydrohalogenation agent. On the .other \hand, if the boiling point of the isocyanate is below the decomposition temperature of the carbamylhalide,

1 then a dehydrohalogenation agent is required. .In either event, however, a dehydrohalogenation agent maybe empl ye (Where the monocarbamyl halide .is the desired .end product, it may be recovered from the gaseous reaction product by any orient ,the procedures described in Patent No. 2,480,088. .to Robert J. lSlocombe and Edgar E.

. R and R are the same or different organic radicals and preferably organic radicals of the classconsisting of aryl,

ara'llryl, alkaryl, alkyl, cycloalkyl and heterocyelic radicals and the substituted derivatives thereof. The substituents contemplated by the instant invention include halogen-, al koxy ,acyle, nitro andother radicals which do not react with hydrogen halides or isocyanic acid esters. 'Iypical examples ofN-monosubstittited ureas which may be sed in thepractice of this invention are phenylurea,

p-tolylurea, m-chlorophenylurea, og-.naphthylure"a, ethylurea, butylurea, octylurea, cyclohexylurea, (methylcyclopentyl)urea and p-bromophenylurea, etc. As illustrative examples of N,N-disubstituted ureas which may be used in which R and R represent different radicals there may be mentioned chlorophenylbutylurea, phenyltolylurea, tolylxylylurea, phenylcyclohexylurea, phenylbutylurea, cyclohexylbutylurea and propylbutylurea.

The separation of the monocarbamyl halide or the corresponding isocyanic acid ester from the reaction product may be effected in any convenient manner and the invention is not limited to the recovery methods herein specifically described. It is to be understood that various modifications may be practiced without departing from the spirit and scope of the invention as defined in the appended claims.

This application is a continuation-in-part of our copending application Serial No. 282,896, filed April 17, 1952, now abandoned.

What we claim is:

1. The method of preparing monocarbamyl chlorides and the corresponding isocyanic acid esters which comprises reacting in the vapor phase hydrogen chloride and a N-substituted urea of the following general formula:

wherein R is a substituent selected from the group consisting of alkyl, cycloalkyl, aryl and halogen derivatives thereof, and R is a substituent selected from the group consisting of hydrogen, alkyl, cycloalkyl, aryl and halogen derivatives of said radicals, said reaction being carried out at a temperature within the range defined by the boiling point of said N-substituted urea and that temperature avoiding substantial decomposition of the isocyanate, and said reactants being employed in a hydrogen chloride/N-substituted urea molar ratio of from about 1:1 up to substantially in excess of 2:1.

2. The method of preparing monocarbamyl chlorides and the corresponding isocyanic acid esters, which comprises reacting, in the vapor phase and at a temperature within the range of about 300 C. to about 500 C., hydrogen chloride and a disubstituted urea of the following general formula:

wherein R is a substituent selected from the group consis ing of .alkyl. encloalkyl, arylaanddialogen derivatiyes hereof, said reactants being employed'iin arhyidrogen euro wherein R is a substituent selected from the group consisting of alkyl, cycloalkyl, aryl and halogen derivatives thereof, to "form a vaporous product containing a i ocyanate including the radical R and unreacted hydrogen chloride and then condensing said vaporous product to recover the corresponding carbamyl chlorideby chemical union of said isocyanate with ,s aid unre actedhydrogen chloride, .said reactants jbeing employed in a hydrogen chloride/disubstituted urea molar ratio of at least 2: 1.

l4. The method of preparing isocyanic acid esters which comprises reactinglin the yapor phase and at .a temperature within the range ofabout300 C. toabout 500- C.,

hydrogen c'hloiideand a disubstituted urea of the following general formula: i

wherein R is a substituentselectedffrom thegroup consisting of alkyl, oycloalkyl,'aryl and halogen derivatives t e eo d a i a e t e re u ing so yanate f om th gaseous P du t a a tempe atu e v d ng s bst n i combinatiowf s i e a ej it he 'i ee itedhydroen chloride. 1

5. The method of preparing isocyanic acid esters, which comprises reacting in the vapor phase and at a temperature within the range of about 300 C. to about 500 C., hydrogen chloride and a disubstituted urea of the following general formula:

wherein R is a substituent selected from the group consisting of alkyl, cycloalkyl, aryl and halogen derivatives thereof, and then separating the resulting isocyanate from the gaseous reaction product while the latter is maintained at a temperature above 90 C. but below the boiling point of said isocyanate, said reactants being employed in a hydrogen chloride/disubstituted urea molar ratio of about 1: 1.

6. The method of preparing phenyl isocyanate, which comprises reacting, in the vapor phase and at a temperature of about 350 C. to about 370 C., hydrogen chloride and N-phenylurea to form a vaporous product containing phenyl isocyanate and unreacted hydrogen chloride and separating said isocyanate from said vaporous product under conditions preventing recombination of said unreacted hydrogen halide with said isocyanate, said reactants being employed in a molar ratio of hydrogen chloride to N-phenylurea which is in excess of that stoichiometrically required to produce said isocyanate.

7. The method of preparing phenyl isocyanate, which comprises reacting, in the vapor phase and at a temperature within the range of about 300 C. to about 500 C., N,N-diphenylurea and hydrogen chloride to form a vaporous product containing phenyl isocyanate and unreacted hydrogen chloride and then separating said phenyl isocyanate by condensing same from said product at a temperature above that at which substantial combination with said unreacted hydrogen chloride occurs, said reactants being employed in a hydrogen chloride/N,N- diphenylurea molar ratio of at least 1:1.

8. The method of preparing phenyl isocyanate which comprises reacting, in the vapor phase and at a temperature within the range of about 300 C. to about 500 C., hydrogen chloride and N,N'-diphenylurea to form a vaporous product containing phenyl isocyanate and timeacted hydrogen chloride and then separating said isocyl anate by condensing same from said product at a temof said phenylisocyanate with said unreacted hydrogen perature above 125 C., said reactants being employed in va hydrogen chloride/N,N'-diphenylurea molar ratio of at least 1:1.

9;. The method of preparing phenyl isocyanate, which comprises reacting, in the vapor phase and at a temperaf ture within the range of about 300 C. to-about 500 C., hydrogen chloride and N,N-diphenylurea to form a va maintained at a temperature above 105 C.,

porous product containing phenyl isocyanate and unreacted hydrogen chloride and scrubbing said isocyanate from said product by means of an inert organic solvent said reactants being employed in a hydrogen chloride/N,N'-diphenylurea molar ratio of at least 1:1.

10. The method of preparing phenylcarbamyl chloride,

'employed in a hydrogen chloride/N,N-diphenylurea molar ratio of at least 2:1.

11. The method of preparing phenylcarbamyl chloride, which comprises reacting, in'the vapor phase and at a 7 temperature of about 350 C. to about 370 C., hydrogen chloride and N-phenylure'a to 'form a vaporous product containing phenyl isocyanate and unreacted hydrogen chloride and condensing said vaporous product to recover the corresponding carbamyl chloride by chemical union chloride, said reactants being employed in a hydrogen chloride/N-phenylurea molar ratio of at least 2:1.

12. The method of preparing ethylcarbamyl chloride, which comprises reacting, in the vapor phase and at a temperature of about 350 C. to about 400 0., hydrogen chloride and N,N'-diethylurea to form a vaporous prodnot containing ethyl isocyanate and unreacted hydrogen "chloride and then condensing the resulting product to recover ethylcarbamyl chloride by chemical combination of the ethyl isocyanate with said unreacted hydrogen chloride, said reactants being employed in a hydrogen chloride/N,N'-diethylurea molar ratio of at least 2:1.

13. The method of preparing cyclohexyl isocyanate, which comprises reacting, in the vapor phase and at a temperature of about 350 C. to about 400 C., hydrogen chloride and, N,N dicyclohexylurea to form a vaporous product containing cyclohexyl isocy'anate and unreacted hydrogen chloride, condensing said vaporous product and thereby recovering cyclohexyl carbamyl chloride by chemical union of said isocyanate and said unreacted hydrogen chloride and then heating said cyclohexyl carbamyl chloride to convert same into the corresponding isocyanate, said reactants being employed in a hydrogen chloride/N,N'-dicyclohexylurea molar ratio in excess of 1:1.

' pounds (1945), page 440. 

2. THE METHOD OF PREPARING MONOCARBAMYL CHLORIDES AND THE CORRESPONDING ISOCYANIC ACID ESTERS, WHICH COMPRISES REACTING, IN THE VAPOR PHASE AND AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 300* C. TO ABOUT 500* C., HYDROGEN CHLORIDE AND A DISUBSTITUTED UREA OF THE FOLLOWING GENERAL FORMULA: 